An analysis of load compensating reflexes in the unrestrained crayfish abdomen is in progress. Flexible suction electrodes are employed to monitor unit activity to the postural extensor and flexor muscles and to record activity of the stretch sensitive muscle receptor organ. These unit activities are monitored during extension and flexion movements of the abdomen under varying conditions of load. Movements are evoked by electrical stimulation of circumesophageal connective premotor interneurons and by tactile stimulation of intact animals. Experiments will also examine the relative contributions of afferent input from the known stretch sensitive elements to reflex load compensation. These experiments will provide detailed information on the manner in which an externally imposed stimulus parameter (the load) affects a small population of interacting neural elements to reflexly generate a compensatory motor output. BIBLIOGRAPHIC REFERENCES: Reed, R.A. and C.H. Page, 1976. Circumesophageal connective control of the common inhibitory motorneuron in the crab, Carcinus maenas. Comp. Biochem. Physiol., (in press). Wyse, G.A. and C.H. Page, 1976. Sensory and central nervous control of gill ventilation in Limulus. Fed. Proc. 35:2007-2012.